multiply by 1/2 and i get the answer i understand how i did this. but what i am asking is every time i do a problem like this do i multiply by 1/2 at the end or it just worked out that way this time? thanks for the help i havent done these in two years so i am a bit rusty

It depends on how many equations there are and what those equations are. Just make sure when you add equations, you add both sides. What you will then get is a new equation that is true; if it ends up that you have 2a1, then divide both sides by 2 (multiply by 1/2), if you have 3a1, then divide both sides by 3, etc.